Acoustic device



E. H. SMYTHE ACOUSTIC DEVICE July 7, 1931.

Filed Nov. 26, 1926 fi i mum.

' and Patented July 7, 1931 UNITED STATES PATENT OFFICE EDWIN H. SMYTHE, OF EVANSTON, ILLINOIS, ASSIGNOR TO WESTERN ELECTRIC COM- IANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ACOUSTIC DEVICE Application filed November 26, 1926. Serial No. 150,830.

This invention relates to acoustic devices lparticularly to sound radiators for loud spea ing receivers and the like.

An object of the invention is to obtain compactness in acoustic devices.

Another object is to radiate sound with substantially equal eficiency in all directions. In accordance with one aspect of the invention the sound radiator comprises a plurality of telescoping sections so related as to constitute a long, tapered continuous passage for sound waves. In accordance with a feature of the invention a sound radiator is provided with an annular mouth so that sound may be radiated therefrom with substantially equal efficiency in all directions. In accordance with another feature, the parts of the structure are so arranged that the device is selfsupporting and is provided with a surface portion which is suitable for supporting external objects. A sound radiator and a useful article of furniture are thereby combined in a single compact structure.

In specific embodiment of the invention herein shown and described, a structure substantially cylindrical in shape is made up of several sections which form a sound passage having a plurality of co-axial portions. The sound passage is sufiiciently long and has a mouth opening of sufiiciently large area that frequencies over a large portion of the audible range may be radiated vvith substantially uniform efficiency. The horn is preferably designed in accordance with the disclosure of British Patent No. 213,528. It is pointed out in this patent that a hornhaving a logarithmic taper will uniformly transmit waves of all frequencies above a definite cut-off frequency determined by the rate of taper and will elliciently radiate all waves whose wave lengths are not greater than three or four tlmes the equivalent diameter of the mouth or bell opening. The walls of the sound passage are preferably constructed of wood, of sufficient thickness that vibrations in the material caused by the transmitted sound become inappreciahle. This is easily accomplished because of the fact that no large fiat surfaces are employed in forming the sound passage.

In the drawings, Fig. 1 is a cross-sectional view of the sound radiator through its longitudinal axis; and

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.

The device, as shown in the drawings, consistsof a member 10 and a member 11, these members being held in fixed spaced relation by means of the rods 16 so as to form a continuous sound passagevhaving three coaxial portions. The lower portion or base 25 of member 10 serves as a support for the whole structure, while the upper portion 26 of the member 11 serves as a support for external objects. An opening in the lower portion of member 10 is provided to receive a sound producer such as the electromagnetic receiver 20, which may be attached to a flange 12 sc cured to member 10/ T he screen 30 is secured to the mouth of the sound passage to prevent objects being placed therein. The inlet portion 13 of the sound passage has a substan tially circular cross-section and, as it approaches the mid-portion of the structure, it leads into a portion 14 of annular crosssection which bends through an angle of approximately 180. A second bend is formed when the sound passage again approaches the base portion of the structure, this angle also being approximately 180. From this point, the annular passage extends upward and terminates in the annular mouth 21. The sound passage is designed so that its cross-sectional area increases progressively from the throat portion to its mouth in acoordance with the exponential law. This holds true for the curved portions of the sound passage as well as for the substan tially straight portions.

What is claimed is:

1. A sound radiator comprising a continuous exponentially tapered sound passage, said sound radiator being formed by a plurality of telescoping sections and having an annular mouth.

2. A sound radiator comprising a continuous exponentially tapered sound passage, having a plurality of portions, all of which are coaxial, and an annular mouth.

3. A sound radiator having a throat portion and a mouth portion, a continuous winding sound passage connecting said throat and mouth portions and comprising a plu- I'ality of circular coaxial portions, the crosssectional area of said sound passage being tapered in accordance with the exponential law continuously from said throat portion to said mouth portion.

4. A sound radiator comprising a substantially cylindrical structure having an exponentially tapered sound passage therein, said sound passage having a substantially annular outlet portion and an axially extended inlet portion.

5. A sound radiator having a throat portion and a mouth portion, comprising a plurality of telescoping sections, a continuous sound passage formed by the inner walls of said telescoping sections for connecting said throat and mouth portions, one of said telescoping sections forming a base for said sound radiator and another of said telescoping sections forming a supporting means.

6. A sound radiator comprising a plurality of telescoping sections, the inner surfaces of which cooperate to form a continuous sound passage, a portion of the outer surface of at least two of said telescoping sections lying in substantially parallel planes.

7. A sound radiator comprising a plurality of telescoping sections forming a continuous sound passage of a. plurality of coaxial portions, and an annular mouth for said sound radiator between two of said telescoping sections. I

8. A horn comprising a plurality of members fitted together to form a sound duct whose rate of increase of cross-sectional areav increases exponentially with the length of the duct, one of said members serving as a support for another of said members.

9. A horn comprising a plurality of sections having orifices therein of such character that when said sections are juxtaposed a sound duct having an exponential variation of cross-section with the length of the duct is formed, certain of said sections being positioned to form a mouth for said horn, annuhr in shape and at substantially right angles to the throat of the horn.

10. A sound radiator comprising two telescoped members of fibrous material, and means for holding said members in spaced relation, said members having curved walls such that a sound duct is formed therebetween the inlet of which is circular in form, the outlet of which is cylindrical in form and an intermediate portion of which is annular 1n form.

In witness whereof, I hereunto subscribe my name this 23 day of November, A. D.

I EDWIN H. SMYTHE. 

